Colloquium: Sam Nariman
Mar 5 @ 3:30 pm – 4:30 pm

Speaker: Sam Nariman (Northwestern U.)

Title: On the homology of diffeomorphism groups made discrete.

Abstract: Let $G$ be a finite dimensional Lie group and $G^{delta}$ be the same group with the discrete topology. The classifying space $BG$ classifies principal $G$-bundles and the classifying space $BG^{delta}$ classifies flat principal $G$-bundles (i.e. those bundles that admit a connection whose curvature vanishes). The natural homomorphism from $G^{delta}$ to $G$ induces a continuous map from $BG^{delta}$ to $BG$. Milnor conjectured that this map induces an equivalence after the profinite completion. In this talk, we discuss the same map for infinite dimensional Lie groups, in particular for diffeomorphism groups and symplectomorphisms. In these cases, we use techniques from homotopy theory to show that the map from $BG^{delta}$ to $BG$ induces a split surjection on cohomology with finite coefficients in the stable range. If time permits, I will discuss applications of these results in foliation theory, in particular, characteristic classes of​ flat surface bundles.

Logic seminar: Mushfeq Khan
Mar 9 @ 2:30 pm – 3:30 pm
Undergrad Seminar: Chris Marks @ Keller 402
Mar 15 @ 3:00 pm – 4:00 pm

Speaker: Chris Marks (Cal State Chico)

Title: Vector-valued modular forms and the bounded denominator conjecture

Abstract: This talk will primarily serve as an introduction to modular

forms, both scalar and vector-valued. After working through definitions

and the group theoretic background, I’ll discuss the so-called Bounded

Denominator Conjecture concerning Fourier coefficients of modular forms.

Logic seminar: Mushfeq Khan
Mar 16 @ 2:30 pm – 3:30 pm
Colloquium: Andreas Weinmann (Hochschule Darmstadt and Helmholtz Center Munich) @ Keller 401
Mar 16 @ 3:30 pm – 4:30 pm

Speaker: Andreas Weinmann (Hochschule Darmstadt and Helmholtz Center Munich)

Title: Variational methods for the restauration of manifold-valued images and data

Abstract: Nonlinear manifolds appear as data spaces in various applications. One example in image processing is diffusion tensor imaging, where the data sitting in every voxel is a positive matrix representing the diffusibility of water molecules measured at the corresponding spatial location. Another example is color image processing, where instead of the RGB representation often other formats such as HSI or HSV are used which employ a circle to represent the hue of a color. A third example are registration problems (e.g., between a camera and an ultrasound devise) where time series of euclidean motions appear. Since the measured data is often noisy, regularization of these nonlinear data is necessary. In this talk, we propose algorithms for the variational regularization of manifold-valued data using non-smooth functionals. In particular, we deal with algorithms for TV regularization and with higher order methods including the TGV denoising of manifold-valued data. We present concrete applications in medical imaging tasks.

Undergrad Seminar
Mar 22 @ 3:00 pm – 4:00 pm
Logic seminar: Amenability and Symbolic Dynamics @ Keller Hall 314
Mar 23 @ 2:30 pm – 3:30 pm

David Webb will continue to discuss results from Adam Day’s paper on amenability and symbolic dynamics.

Colloquium: Christopher Marks (Cal. State Chico)
Mar 23 @ 3:30 pm – 4:30 pm

Speaker: Christopher Marks (Cal. State Chico)

Title: Vector-valued modular forms and CM Jacobians

Abstract: In this talk, I will explain how vector-valued modular forms

may be used to compute explicitly periods of modular curves, and how the

application of this technique to noncongruence subgroups of the modular

group should soon yield new examples of Jacobians of modular curves with

complex multiplication (i.e., CM Jacobians).